257 



THE BRITISH NATURALIST. [December 



writers in articles scattered tlirough several publications. — W. A. 

 Gain. 



Unio ])ictoviiin VRY. major, G3.in. — In the "British Naturalist"' for 

 November, Mr. Gain describes a var. major oi Unio pictorum. I would 

 point that the U . poiiderostcs, Spitzi in Rossni., Icon., XII., p. 31., T. 

 59, F. 767, (1844), has priority, for it is but a variety of U. pictorum, 

 and is regarded as such by Droiiet, in his " Monag. des Unio de la 

 France," (Mem. d. 1. Soc. d' Agricult. d. Sci. &c., T. VIIL, No. 

 41-42, Troyes, 1887). — Waller E. Collinge, Mason College, 

 Birmingham. 



Mr. J. Sherriff Tye has written to the same effect. —W. A. G. 



RissoA MEMBRANACEA, Adams : — Synonyms: R. labiosa, Montg., 

 R. fyngilis, Mich., Turbo costatus, Pult., R. pulla,, Brown, and 

 probably many others. — It belongs to the subgenus Zippora, Leach — 

 a manuscript name of Leach's, published by Gray in 1847, with the 

 well-known R. auriscalpium L., of the Mediterranean, as type, This 

 name is a convenient artificial group for Rissons with a particularly 

 1 ongated form and reflected lip — the latter characteristic as in the 

 members of what is generally considered the typical group (R. parva, 

 violacea, etc). The shells in § Zippora are usually ribbed lengthways, 

 but each species seems to have occasional exponents with these ribs 

 either very indistinct or quite obsolete. Compare th^ similar varieties 

 in nearly all members of the typical -group,, e.g. R. parva v. interrupta, 

 R. violacea v. ecostata, R. albella v. sarsii, etc. The type of the group 

 given by Tryon* is according to MM. Bucquoy and Dautzenberg f a 

 species of Acme, and no Rissoa at all. So much for the group, of 

 which the species in the heading is our sole British representative. 

 It is a somewhat local species, though occurring on many parts of the 

 coast, and is to be looked for at low water on various seav/eeds, 

 Zostera, etc. I have found in Guernsey that it seems to affect the 

 spongy green weed called Codiuni tomentosum, in company with 

 R. parva. Shells on this weed are always especially clean and fine. 

 While speaking of this Codium, I may may mention that in Guernsey, 

 at any rate, it seems to be the exclusive haunt of that lovely little 

 green Nudibranch, Elysia viridis Montg., which there occurs plentifully, 

 mimicking the colour of the weed to a nicety, and not easy for an 

 inexperienced eye to " spot." The size of R. memhranacea, to begin 

 with, will serve to distinguish it from any of its congeners. It is the 

 largest British Rissoa, averaging 8 mm. in length. There is also on 

 the pillar a solid tooth, or fold, which is not found in our other 

 species ; the colour is whitish, with a tinge of yellow or browm, and at 



* Struct, and Syst. Conch. II , 263. f Moll, du Rouss. I., 276. 



